1. Field of the Invention
The present invention generally relates to an image projection apparatus and method, and more particularly, it relates to an image projection apparatus and method for projecting red (R), green (G), and blue (B) beams separated from a holographic optical element onto a screen by using a galvanometer. The present application is based on Korean Application No. 2001-77650, filed on Dec. 8, 2001, which is incorporated herein by reference.
2. Description of the Prior Art
Display apparatuses like projectors and projection systems display an image by projecting the received image signals onto a screen. Such display apparatuses are widely used, for example, in business meetings, movie theaters and home theaters.
Conventionally, images appearing on a liquid crystal display (LCD) or a cathode ray tube (CRT) are magnified by a lens and then projected onto a screen. As this approach only magnifies the images, it cannot provide a good quality image. In order to alleviate this drawback, an image projection apparatus having a digital micromirror device (DMD) panel is used.
The DMD is a semiconductor optical switch using a micromirror. The micromirror regulates the reflection of light in accordance with the input image signals. The DMD provides advantages such as excellent color representation and high light intensity. Further, as there is no need for analogue-to-digital or digital-to-analogue conversion, a relatively clear image can be obtained. Additionally, as there is no loss of light due to a polarizing filter, the DMD can obtain high optical output.
FIG. 1 shows the basic structure of a conventional image projection apparatus using a color wheel.
Referring to FIG. 1, the conventional image projection apparatus 100 using a color wheel includes a light source 110, a color wheel 120, a DMD panel 130 and a projection lens 140. The optical path of the white light is indicated by the one-dotted line in FIG. 1.
The light source 110 irradiates white light using, for example, an arc lamp or a laser beam. The color wheel 120 is rotated by a separate rotating means (in the direction of the two arrows), and is subdivided into red (R), green (G) and blue (B) regions.
White light from the light source 110 is subdivided into RGB beams by the RGB regions.
The DMD panel 130 has a plurality of micromirrors 130a. Divided by respective wave lengths, the RGB beams are projected onto the DMD panel 130 and deflected from the micromirrors 130a. The deflected RGB beams pass through the projection lens 140, and are displayed on the screen as an image.
However, in the conventional image projection apparatus 100, G and B beams are absorbed or reflected in the R region, while the R beam is passed therethrough. The same phenomenon is found in the G and B regions corresponding to the G and B beams. Accordingly, only a third of the white light can be utilized by the color wheel method, which results in a deterioration of brightness of the image by two thirds.
In other words, when using the color wheel 120 for colorization, white light from the light source 110 loses light quantity while passing through the color wheel 120. Accordingly, light efficiency deteriorates, and maximization of the brightness of the image on the screen cannot be expected.
Accordingly, it is an aspect of the present invention to provide an image projection apparatus for realizing an image by scanning a monochromatic light separated from a holographic optical element with a galvanometer.
The above aspect is accomplished by an image projection apparatus and method according to the present invention, including a light source for irradiating a white light; a light separating unit for separating the white light into monochromatic lights of different wavelengths, and forming a plurality of monochromatic color stripes; a galvanometer for reflecting the plurality of monochromatic color stripes by a predetermined angle; a digital micromirror device (DMD) panel for receiving the reflected monochromatic color stripes, transforming the received monochromatic color stripes, and reflecting the transformed stripes by a predetermined angle; and a projection lens disposed opposite to the DMD panel.
The light separating unit includes a square beam generating unit for transforming the white light into a square beam; a linear beam generating unit for transforming the generated square beam into a linear beam; and a color separating unit for separating the generated linear beam into the plurality of monochromatic color stripes.
The linear beam generating unit comprises a cylindrical lens that linearizes the square beam. The color separating unit comprises a holographic optical element that separates the linear beam into red, green and blue stripes.
The galvanometer includes a reflective mirror having one reflective surface; and a driving unit for driving the reflective mirror so that the reflective mirror oscillates between a first position and a second position. The reflective mirror in the first position projects one or more monochromatic color stripes to an upper end of the DMD panel, and the reflective mirror in the second position projects one or more monochromatic color stripes to a lower end of the DMD panel.
The reflective mirror reciprocally oscillates between the first and second positions by the driving unit at least once, realizing a down-scanning screen by oscillating from the first position to the second position, and realizing an upscanning screen by oscillating from the second position to the first position. The projection lens concentrates the incident light from the DMD panel, and projects the concentrated light to a display device.
Additionally, it is an aspect of the present invention to provide an image projection method for realizing an image by irradiating a white light. The white light is then separated into a plurality of monochromatic lights of different wavelengths, whereby a plurality of monochromatic color stripes are formed from the monochromatic lights. The image projection method further includes reflecting the plurality of monochromatic color stripes by a predetermined angle, receiving the reflected monochromatic color stripes, and transforming the received monochromatic color stripes. The transformed stripes are then reflected by a predetermined angle, wherein a projected image is realized by a projection lens disposed opposite to a digital micromirror device (DMD) panel.
In accordance with the present invention, the quantity of light increases, the light efficiency improves, and the brightness of the realized image is enhanced.